Underfloor heating distance, missing spot, and bathtub

Basically yes. But not if the room to be heated to a higher temperature is laid out tightly or if wall surfaces are also heated

That is exactly why the planning of the underfloor heating is important. You then do the hydraulic balancing yourself in the first winter and disable the individual room control. With poor planning, you won't get the balancing done properly. Also make sure that no buffer tank is installed for you. Buffer tanks, ERR, and high flow temperatures are the easy alternative to good planning.

But infrared then into the mirror or ceiling or wall?

I don't know what is best there. Not opposite a window. There are solutions for the mirror.

have the underfloor heating calculation handed over to you or ask who created it. Your installer or did he only forward it to the manufacturer of the underfloor heating pipe? If it’s the latter, you can basically throw it in the trash